Whisker, a beloved river otter at the Detroit Zoo, passes away at the age of 21

The Detroit Zoo said on Tuesday that Whisker, a beloved North American River otter, passed away at the advanced age of 21.

According to the zoo, Whisker was rescued when she was a pup in 2003 and came to the zoo in 2009.

Shortly after her arrival, Whisker and male otter, Lucius, became inseparable and in 2012, became the parents of the first river otter litter to be born at the zoo in 50 years.

The median life expectancy for river otters is 12 years, according to the zoo.

"Whisker was a superb mother. She was also very smart and quick to catch onto training. She was a favorite among her caretakers, who bonded deeply with her over the years," according to the zoo.

As she got older, Whisker had a decline in the function of her hindlimbs and had mobility issues and discomfort.

Her care team worked to develop ways to prolong her quality of life, but they came to the decision to humanely euthanize her.

"She was truly an amazing otter and will be dearly missed by all," the zoo said.

In January, the zoo said that Ollie, a sea otter at the zoo, passed at the age of 13 away after a "brief and sudden illness."

There are still two sea otters at the Arctic Ring of Life – Monte and Finn, and three otters in the Edward Mardigian Sr. River Otter Habitat – Lucius, Gus and Kalee.